Such climatic apparatuses consume energy, generally of electrical origin, which electrical energy is used directly to produce heat, for example by the passage thereof through an electric resistance heater, or by means of a heat engine such as a heat pump or a refrigeration unit for producing heat or cold. The invention is not limited to climatic apparatuses operated by means of electrical energy and also applies to any heat engine or climatic apparatus operated by means of combustion.
The energy demand emanating from climatic apparatuses is not uniform throughout the day, week or year. For example, in an urban area, peak periods are observed, when both offices and dwellings are occupied, for example at the end of a weekday day. The demand also changes with the seasons, with winter peaks in temperate countries, and summer peaks in hot countries. These consumption peaks alternate with off-peak periods, where the energy consumption is reduced. This lack of uniformity of the consumption is particularly tricky to manage when the energy consumption is electric and when it cannot be stored as such. The situation is more particularly tricky when the energy production uses uncontrolled intermittent production means, such as wind or solar means. Both the peak periods and off-peak periods pose a problem.
In a dwelling, the pricing system for the energy consumption tends to encourage consumption during off-peak hours and to discourage consumption during peak hours. Thus, in order to benefit from the best tariff but also in order to reduce the carbon footprint of said dwelling, it is useful to be able to store and restore the energy, particularly the energy consumed by the climatic apparatuses.
Heat storage techniques are known from the prior art and are based essentially on two principles, whether it is a question of storing cold or heat:                sensible heat storage;        latent heat storage.        
Sensible heat storage consists in bringing a body, generally having a high thermal inertia, for example sand, to a high temperature, or conversely to low temperature in order to store cold, in an off-peak period, then in restoring this heat to the premises to be heated or to be cooled in a peak period, using a heat transfer fluid, for example by blowing into said premises air that has been in contact with the body in question and that is heated or cooled by this contact. Sensible heat storage makes it possible to store, in a body of mass m, of specific heat capacity Cp (constant with temperature), brought from an initial temperature T1 to a temperature T2, an amount of heat Hs equal to:Hs=m·Cp·(T2−T1)
Latent heat storage uses a material which, under the effect of heating or cooling, undergoes a phase transition, said phase transition taking place with the absorption, on heating, or the restoration, on cooling, of a latent heat of transition. The phase transitions most used for this purpose are the solid-liquid phase change, referred to as melting, crystallization or solidification phase change, the liquid-gas phase change, referred to as evaporation, liquefaction or else condensation phase change. Thus, taking the example of a melting phase change of a body of mass m, having a melting temperature TF such that T1<TF<T2, having a heat capacity Cps in the solid state and Cpl in the liquid state and having a latent heat of transition L per unit of mass, when this body is heated from a temperature T1 to a temperature T2, the amount of energy HI stored is:HI=m·Cps·(TF−T1)+m·L+m·Cpl·(T2−TF)
For a same mass of material, the amount of energy stored is significantly greater, since the latent heat is generally high. For example, the latent heat of melting 1 kg of ice is equivalent to the energy needed to heat 1 kg of water from 0° C. to 80° C.
Since the phase transition is reversible, the amount of energy HI is restored during the cooling and the solidification of the body.
Thus, the storage of thermal energy in the latent heat of transition, by means of a material having a phase transition is, generally, much more effective than sensible heat storage. However, this thermodynamic principle encounters practical difficulties.
A first difficulty is linked to obtaining a uniform temperature in the body that is the subject of the phase transition. Indeed, the phase change materials (PCM) are not by themselves good heat conductors. Thus, when the heat transfer fluid intended to extract the latent heat therefrom, for example air, sweeps over the surface of the block, the thermal resistance that accumulates between the external exchange surface and the state change front rapidly becomes predominant and limits the thermal power.
One solution from the prior art for limiting this phenomenon consists in increasing the exchange surface by encapsulating the PCM so as to increase the specific exchange surface. This encapsulation is carried out in microbeads or in textile fibers. Besides the cost of these materials, this method from the prior art also has implementation drawbacks.
Thus, during the cooling of a solid-liquid transition PCM and on passing the melting temperature, whether this is for storing cold or for restoring heat stored in the liquid phase, a supercooling phenomenon occurs. This phenomenon is expressed by the fact that the solidification temperature is shifted toward low temperatures with respect to the melting temperature. Thus, the liquid phase does not solidify even for temperatures significantly below the melting temperature. Yet, the use of the latent heat of transformation means that the transformation and the change of state occur. Experimentation shows that the smaller the amount of PCM, the greater the supercooling. Thus, the solution from the prior art that consists in separating, by encapsulation, the PCM into small amounts is disadvantageous from the point of view of supercooling.